As computers become more prevalent in everyday use, particularly personal type computers, users are employing them in a variety of different situations. Depending upon the particular situation, the user may desire to change the configuration of the display devices connected to the computer. For example, portable computers of the so-called laptop or notebook type have become increasingly popular because of their small size and light weight, making them suitable for use while traveling. Due to the need to keep their dimensions to a minimum, the display screens built into such computers are relatively small in size, and may offer only limited display capabilities. Therefore, when using one of these types of computers in an office environment, the user may connect it to a monitor having a larger display area and/or enhanced display capabilities. Such a connection might be made, for example, by means of a docking station which enables the portable computer to be conveniently connected to a variety of peripheral devices, or by inserting a video card in a PC Card slot.
Subsequently, the user might remove the added monitor, for example to take the computer home or to use it while traveling. In this situation, the built-in display screen must be used. In other words, the computer must route all information to be displayed to the built-in screen, rather than the port to which the external monitor was connected. In addition, the displayed information must be reformatted, or otherwise processed, to accommodate the display parameters of the built-in device.
In the past, changes in the configuration of the computer system, such as the addition or removal of display devices, only became effective upon a restart, or reboot, of the computer system. As part of its initial startup procedure, the computer's operating system detects the presence of each device driver loaded on the system, and registers each such detected driver to permit communications to be carried out between the operating system and the device with which the driver is associated. If a new device and corresponding driver are added to the system after this initialization procedure, the driver is not registered with the operating system, and therefore communications do not take place until the operating system goes through its initialization procedure again, e.g. upon the next reboot of the computer. Hence, if a user adds a monitor to the computer system, the monitor cannot be used to display information generated by the computer until it has been rebooted.
U.S. Pat. No. 5,682,529 discloses a system for dynamically accommodating changes in the display configuration of a computer, without the need to restart the computer. In the system of this patent, changes can be made to the display environment for a computer system while it is in a sleep mode, in which the computer's central processing unit is maintained in a minimal operating state. When the computer is "awakened" from this sleep mode, the system of the '529 patent enables the changed configuration to be immediately recognized, and thereafter utilized in the display of information generated by the computer.
As the capabilities offered by personal computers continue to expand, the opportunities for changing the configuration of computers grows in a concomitant manner. In some situations, users may desire to have changes in the configuration of the computer's display environment become instantaneously effective, without the need to restart the computer or even place it in a sleep mode. For example, the user may create a slide presentation on a notebook computer. During the course of a meeting, a user may desire to immediately display the slide presentation, by connecting the computer to a suitable video projector, or the like. It is desirable to be able to carry out this operation without the need to first put the computer to sleep, and thereby reduce the time needed to operate within the changed configuration. It is an objective of the present invention, therefore, to expand upon the capabilities of the system of the '529 patent, by providing a display environment in which so-called "hot plugging" of displays is possible, wherein a display becomes immediately available for use as soon as it is plugged into the computer system.